Sawshark
The sawshark or saw shark is an order (Pristiophoriformes) of sharks bearing a unique long, saw-like rostrum (snout or bill) edged with sharp teeth, which they use to slash and disable their prey. There are eight species within the pristiophoriform family including the longnose or common sawshark (Pristiophorus cirratus), shortnose sawshark (Pristiophorus nudipinnis, Japanese sawshark (Pristiophorus japonicas), Bahamas sawshark (Pristiophorus schroederi), sixgill sawshark (Pliotrema warreni), African Dwarf Sawshark, Lana's Sawsark and the Tropical Sawshark (Pristiophorus delicatus). The sawshark is found in many areas around the world, but is most commonly found in waters from the Indian Ocean to the Southern Pacific Ocean. They are normally found depths around 40–100 m, but can be found at much lower depths in tropical regions. The Bahamas Sawshark was discovered in deeper waters (640 m to 915 m) of the northwestern Caribbean. Description and Behavior Sawsharks of all species have a pair of long barbels about halfway along the snout. They have two dorsal fins, but lack anal fins. The genus Pliotrema has six gill slits, and Pristiophorus the more usual five. The teeth of the saw typically alternate between large and small. Sawsharks reach a length of up to 5 feet and a weight of 18.7 pounds with females tending to be slightly larger than males. The body of a longnose sawshark is covered in tiny placoid scales: modified teeth covered in hard enamel. The body is a yellow-brown color which is sometimes covered in dark spots or blotches. This coloration allows the saw shark to easily blend with the sandy ocean floor. These sharks typically feed on small fish, squid, and crustaceans, depending on species. They navigate the ocean floor using the barbels on the saw to detect prey in mud or sand, then hit prey with side-to-side swipes of the saw, crippling them. The saw can also be utilized against other predators in defense. The saw is covered with specialized cells, ampullae of Lorenzini which detect an electric field which is given off by buried prey. Sawsharks have a relatively slow life history. Mating season occurs seasonally in coastal areas. Sawsharks are ovoviviparous meaning eggs hatch inside of the mother. They have litters of 3-22 pups every 2 years. After 12 months of pregnancy, the pups are born at 30 cm long. It is interesting to note that while in the mother, pups teeth are inverted into their mouth to avoid harm. The sharks care for their young until they are sexually mature at 2 years of age and at which point can fend for themselves. Saw sharks typically live more than 15 years in the wild They can be found living in solitary or in schools. Conservation Among the different species of saw shark, all are listed on the IUCN Red List of 2017 as either data deficient or of least concern. Sawsharks generally do not see much human interaction because of their preferences for deep habitats. Differences between sawsharks and sawfish Sawsharks and sawfish are cartilaginous fish possessing large saws. These are the only two families of fish that have a long blade-like snout. Although they are similar in appearances, saw sharks are distinct from sawfish. Sawfish are not sharks, but a type of ray. The gill slits of the sawfishes are positioned on the underside like a ray, but the gill slits of the sawshark are positioned on the side like those of a typical shark. Sawfish can grow to a much larger size (upwards of 20 feet in the largest species), lack barbels, and have evenly sized teeth rather than alternating sized teeth of the saw shark. A clear difference is that a sawfish has no barbels and a sawshark has a prominent pair halfway along its rostrum. The sawshark uses these like other bottom fish, as a kind of antennae, feeling the way along the ocean bottom until it finds some prey of interest. Both the sawshark and the sawfish utilize the electroreceptors on the saw, known as the ampullae of Lorenzini, to detect the electric field given off by buried prey. Genuses and Species There are two genera of sawshark, with eight species. * Genus Pliotrema ** Pliotrema warreni ''(Sixgill sawshark) '' * Genus Pristiophorus '' ** ''Pristiophorus cirratus (Longnose sawshark) ** Pristiophorus delicatus (Tropical sawshark) ** Pristiophorus japonicus (Japanese sawshark) ** Pristiophorus lanae (Lana's sawshark) ** Pristiophorus nancyae (African dwarf sawshark) ** Pristiophorus nudipinnis (Shortnose sawshark) ** Pristiophorus peroniensis (Eastern Australian sawshark) ** Pristiophorus schroederi (Bahamas sawshark) Category:Chondrichthyes Category:Elasmobranchs Category:Sharks Category:Sawsharks